The present disclosure relates generally to testing and evaluation of subterranean formations, and, more particularly, to methods and apparatuses for testing and evaluating subterranean formations using pressure pulses.
Formation pressure is fundamental in assessing the hydrocarbon yield of a reservoir. Without an estimate of the formation pressure, there is a great deal of uncertainty in a fields' development and the investment required. Virtually all the methods used to calculate the net amount of recoverable hydrocarbon are highly dependent on the initial formation pressure. Field-develop optimization also depends on formation-pressure estimates to verify reservoir depletion and delineate the producing intervals' connectivity.
There have been attempts to find the fundamental properties of tight sand, shale gas, and heavy-oil reservoirs. However, studies on the pressure-transient analysis methods applied to packer and probe-type formation testing have rarely been reported. When a typical draw-down and build-up test is applied, the pressure transient takes too much build-up time to resolve using conventional analysis or a history match to be of practical value in these very low-mobility reservoirs.
Another complication for testing in tight formations is that the measure pressure is supercharged and is greater than the reservoir pressure. The measured shut-in pressure is usually assumed to be the formation pressure. In a permeable formation, mudcake can form quickly and is normally very effective in slowing down invasion and maintaining the wellbore sandface pressure to near that of the formation pressure. However, in low mobility formations, in which there could be no sealing mudcake to isolate the reservoir from hydrostatic pressure, this assumption is unrealistic. In tight formations, the invasion rate is slowed by the formation, and mudcake may form slowly or it may not exist. Therefore, the measured pressure in these cases is substantially greater than the formation pressure as a result of the lack of sealing mudcake.
While embodiments of this disclosure have been depicted and described and are defined by reference to exemplary embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.